The invention relates to a device for collecting and separating particles and microorganisms present in ambient air, for the purposes of identifying and counting such particles and microorganisms.
It is important to perform such identification and counting in numerous fields such as the pharmaceutical industry, the food industry, medical settings, hygiene services, veterinary services, site monitoring, etc., with the dimensions of the particles and microorganisms for collection lying in the range 0.5 micrometers (μm) to several tens of micrometers.
Document FR-A-2 855 831 discloses a device of this type that includes a removable centrifuging enclosure associated with air suction means, the enclosure having an air inlet and an air outlet and forming a container for transporting a liquid sample containing the collected particles and microorganisms.
It is desirable to be able to vary the sample-taking characteristics applied to particles and microorganisms as a function of the conditions in which such samples are taken, and for example:                indoors or outdoors;        for monitoring purposes that are continuous, or over a long duration, or in the event of an alarm;        as a function of the characteristics of the microorganisms being collected.        
In the event of an alarm, it is desirable in particular to take samples at a high rate of suction in order to obtain a result as quickly as possible. Conversely, when taking samples for monitoring purposes it is possible to use a lower rate over a longer period of time.
Similarly, relatively low suction rates are more suitable for preserving certain microorganisms.
At present there are no apparatuses in existence for collecting and separating particles and microorganisms present in ambient air and in which it is possible to cause the suction flow rate to vary over a large range under conditions that maintain the quality and the reliability of the samples taken.